1. Field of the Invention
The present invention relates to photographic sensitive materials having an improved antistatic property and, particularly, to photographic sensitive materials having an excellent antistatic property which comprise a nonionic polyoxyethylene surface active agent and at least one of a thiocyanate, iodide, perchlorate and periodate in at least one layer.
2. Description of the Prior Art
In photographic sensitive materials, photographic light-sensitive emulsion layers and, if necessary, layers composing the photographic sensitive material, such as an intermediate layer, a protective layer, a back layer and an antihalation layer, etc., are provided on one or both surfaces of a base such as a film of a poly-.alpha.-olefin such as polyethylene or polystyrene, a cellulose ester such as cellulose triacetate, or a polyester such as polyethylene terephthalate, paper, synthetic paper or a paper sheet both surfaces of which are coated with said high molecular materials, through a subbing layer which is provided in order to firmly bond the base to the photographic emulsion layers.
As photographic sensitive materials in which photographic emulsions are applied to both surfaces of the base there are, for example, direct X-ray films. In most other photographic sensitive materials, the photographic emulsions are generally applied to only one surface of the base.
Accordingly, in the latter case, there is one face to which the photographic emulsions are not applied, namely, the base surface which is generally referred to as the back face. Since the photographic sensitive materials are composed of a base having an electrically insulating property and photographic layers, electrostatic charges often accumulate as a result of contact and friction between surfaces of the same or different materials or separation thereof in producing the photographic sensitive materials or upon use.
The accumulated electrostatic charges create many troubles. For example, in the photographic films before development processing, the photosensitive emulsion layers are exposed to light by discharging the accumulated electrostatic charges whereby dot spots or branch-like or feather-like specks are formed when the photographic films are developed. They are so-called static marks by which the commercial value of the photographic films remarkably diminishes and sometimes is completely lost. For example, if they appear on medical or industrial X-ray films they may result in erroneous diagnosis. Since these marks are not revealed until development, it is one of the most troublesome problems. Further, the accumulated electrostatic charges bring adhesion of dust to the surface of the film, by which secondary troubles such as uneven coating at application, etc., result.
Such electrostatic charges often accumulate when the photographic sensitive materials described above are produced or used. For example, the electrostatic charges may be generated by friction due to contact of the photographic film with rolls during production, or by separation of the emulsion face from the base face in the step of winding and rewinding the photographic film. Further, in finished goods, the electrostatic charges may be generated as the emulsion face passes over the base face during rewinding of the photographic film under high humidity conditions sufficient to cause adhesion, or they may be generated by contact or separation of the X-ray film with mechanical parts or a fluorescent sensitizing paper in an automatic camera. Further, charges may be generated by contact with packing materials. Static marks on the photographic sensitive materials induced by accumulation of the electrostatic charges remarkably increase with an increase in the sensitivity or the processing rate of the photosensitive materials.
Though it is believed that charges originating by contact and the charges originating by separation result from an ionic interaction between the molecules of the contacting materials, it is difficult at the present time to surmise what material charges are positive and what material charges are negative. However, it is clear that such charging can be prevented, if the electric pressure is reduced or if conductivity of the surface of the material is increased so as to remove the electrostatic charge in a very short time before the electrostatic charge accumulates and partial discharging occurs.
Therefore, it has been hitherto proposed to increase the conductivity of the base or the coating surface layer of the photographic sensitive materials, and various hygroscopic materials or water-soluble inorganic salts, certain surface active agents and polymers, etc., have been used to this end. For example, polymers described in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291 and 3,615,531, surface active agents described in British Pat. No. 861,134 and U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972 and 3,655,387, and zinc oxide, semiconductors and colloidal silica described in U.S. Pat. Nos. 3,062,700, 3,245,833 and 3,525,621 have been used to increase the conductivity of the base or the surface.
As a method of rendering the base of a photographic film antistatic directly, the above-described materials have been incorporated directly in a polymeric material and used as the base or they have been applied to the surface of the base. In the latter case, the antistatic agent is applied to a back layer alone or together with a polymer such as gelatin, polyvinyl alcohol or cellulose acetate, etc. Further, antistatic agents have been incorporated in a photographic emulsion layer or a surface protective layer and an aqueous solution of the antistatic agent has been applied to the surface of said layer to impart antistatic properties to the material. However, many of these materials are useful with only one kind of film base or photographic composition. Though some of these agents produce good results on a specific film base or photographic emulsion or on other photographic elements, they do not prevent charging on other film bases or photographic elements and sometimes they have a bad influence on photographic properties.
Generally, for high speed emulsions, there are a small number of materials which show a satisfactory antistatic effect under low humidity (30% RH or less), but the antistatic effect deteriorates and adhesion problems result under a high temperature and a high humidity. Particularly, in sensitive materials in which a photographic emulsion is applied to both surfaces of the base, such as direct X-ray sensitive materials, it is difficult to establish techniques for effectively utilizing the antistatic agents. Further, in case of searching for antistatic agents used for photographic sensitive materials, it is necessary to take into consideration not only photographic properties of photographic emulsions (such as sensitivity, fog, granularity or sharpness, etc.), but also coefficient of friction, good camera behavior and a good anti-adhesive property, etc.